The present invention relates to systems for aiming a beam of light from a moving vehicle, such as a space vehicle, in a desired direction which is specified by celestial or geographic coordinates. In general, a highly collimated light beam such as a laser beam is directed by a pointing mirror which is mounted in a known orientation on the spacecraft. One method of aiming such a laser is to use the attitude control system of the craft to re-orient the craft such that a fixedly mounted pointing mirror is directed in the desired direction. The spacecraft orientation is established by an independent sensing system. Another method of aiming, which also relies on the spacecraft attitude sensor, is to mount the pointing mirrors in a steering assembly, and move the assembly to point in the desired direction based on the known spacecraft attitude, the fixed mounting Position of the mirror, and the initial mirror orientation with respect to the fixed mount.
A number of pointing inaccuracies may arise in such systems due to errors in the spacecraft attitude determination which may result, e.g., from limitations of the horizon sensor, sun seeker or other sensors employed in that determination. Further errors may result from the pertubations in mounting alignment of the attitude sensors with respect to the spacecraft, of the laser cavity mirrors with respect to the spacecraft, and of the base of the pointing mirror with respect to the spacecraft. The pointing accuracy is also affected by the zero adjustment and stability of the mirror angle transducers.
Given the extreme thermal gradients possible in a space environment, the cumulative effect of these different errors in sensing or alignment may be significant. Accordingly, it is desirable to provide a laser pointing system of enhanced accuracy.